Knife switch with closure resisting and shielding spring



J y 1965 E.. J. NIELSEN ETAL 3,

KNIFE SWITCH WITH CLOSURE RESISTING AND SHIELDING SPRING Filed Oct. 16, 1962 a 71 INVENTQR. M 8. 3,4 BY

W ATTORNEY.

United States Patent 3,194,930 KNIFE SWiT-CH WITH (ILGSURE RESESTTVG AND SHHELDTNG SPRING Erik J. Nielsen, Mention, and Robert D. Boley, Milwautree, Wis assignors to Square D Company, Park Ridge,

23., a corporation of Michigan Filed Oct. 16, 1%2, er. No. 230,961 9 Claims. (Cl. 200-158) This invention relates to knife switches, and particularly to a knife switch for use in disconnecting terminal blocks.

For the purposes of illustration, the invention will be shown as embodied in a terminal block adapted for incorporation in an electrical terminal strip of the type disclosed in United States'Letters Patent No. 2,981,922 of Herman L. Van Valkenburg and Erik J. Nielsen, issued April 25, 1961, its use in other terminals and for other purposes being readily apparent from the illustrative example.

In terminal strips of the character disclosed in the above patent, it is desirable at times to open the circuit between the terminals of the block temporarily; for example, for servicing equipment on a power line which is connected to a source through the block. The danger of making and breaking a circuit through a conductor of a terminal block by disconnecting the wire ends from the conductor terminals are well known. For such purposes, a knife switch may be provided on the block so that the circuit from one terminal to the other can be interrupted without the necessity of disconnecting the wires of the line from the terminals, thereby eliminating the dangers of having loose, live wire ends exposed. However, in switches of this character, there is always danger that, while one is working on a line, vibrations imposed on the block from extraneous sources at the site of use may cause closure of the knife switch with consequent dangers to personnel and equipment.

One object of the present invention is to provide a disconnect knife switch which can be opened readily for interrupting the circuit between the terminals of a disconnect terminal block and can be closed readily and drawn firmly into final closed position for efiecting a tight contact, and which has an electrically insulated finger grip and shield for shielding against accidental touching of the bare blade and its support by the fingers of an operator during operation of the switch.

Another object is to provide on such a blade, in combination with the finger grip, a yieldable leaf spring for yieldably restraining the switch from movement from an open to a closed position by the usual vibrations encountered at the work site where the block is installed, and which leaf spring is of electrically insulating material and acts as a shield for guarding against accidental contact with the blade.

Another object is to provide, on the blade, a screw for drawing the lade into firmly closed position and a retainer held in place by the finger grip for holding the screw captive to the blade when the screw is unconnected to the stationary contact of the switch and the blade is in open position.

Various other objects and advantages will become apparent from the following description, wherein reference is made to the drawing, in which:

, a blade 13 having a free contact end 13a.

Bdfidfifid Patented July 13, 1%65 "ice FIG. 1 is a top plan view of a terminal block of a terminal strip with the switch of the present invention incorporated therein;

FIG. 2 is a front elevation of the terminal block and switch illustrated in FIG. 1;

FIG. 3 is a right end elevation of the terminal block and switch illustrated in FIG. 2;

FIG. 4 is a front elevation, similar to FIG. 2, showing the switch in a partly open position;

FIG. 5 is a view similar to FIG. 4 showing the switch in a maximum opened position;

FIG. 6 is an enlarged front elevation of the insulating finger grip of the invention, including parts integral therewith, parts thereof being shown in section to illustrate the manner of connecting it to the switch blade;

FIG. 7 is a right end elevation, partly in section, of the finger grip and parts illustrated in FIG. 6; and

FIG. 8 is an enlarged sectional view taken on the line 8-3 in FIG. 6.

Referring to the drawings, the block comprises a moldcdbody 1 of electrically insulating material, such as nylon or synthetic organic plastic. The body has a base 2 with a slot '3 arranged to receive a supporting rail for supporting the body as part of an electrical terminal strip, such as described in the identified patent. The block has the usual upright barrier wall 4.

Mounted on the body is an electrical terminal conductor 5 provided with a screw 6 by which the terminal of a wire can be readily connected thereto. The terminal 5 has a spacer portion 7 which terminates at its upper end into a stationary contact 8. The stationary contact 8 has a threaded aperture 9 for receiving a screw for securing the blade of the switch in closed position, as will later be described. Also carried by the body is a conductor terminal Til having a screw 11 for connecting the terminal of a wire thereto. The conductor terminal 10 is provided with a pair of yoke arms 12 for supporting The other end of the switch blade 13'is secured to the arms 12 by a pivot 14 for swinging generally edgewise to dispose the free end 13a of the blade into and out of contact with the contact 8. The free end 13a of the blade is twisted into a plane at right angles to the plane of the remainder of the blade so that the free end is in fiatwise face to face relation with, and can seat firmly on, the upper face of the stationary contact 8. The free end 13111 of the blade has an aperture 15 in which a washer head screw 17 is accommodated with its shank protruding from the for- Ward face of the blade for entering the aperture 9 of the stationary contact 8, for threaded cooperation therewith when the blade is closed. The screw is operable for drawing the free end of the blade into firm contact with the contact 8. The screw 17 has a head 18 disposed at the rear of the free end 13:: of the blade. Thus, upon loosening the screw, the blade can be released from the contact 8 to permit opening of the switch, whereupon the blade can be moved to an open position such as shown in FIG. 4, or the maximum open position shown in FIG. 5, or positions therebetween.

As mentioned, it may be that vibrations occurring at the work site may cause the switch blade to close accidentally and it is desirable to assure that it will not be so closed. Further, it is desirable that the proper screw 17 be used for securing the blade firmly in closed position so screw 17 which must remain 3 as to prevent thread stripping and insecure contact. Again, it is desirable to reduce the dangers of the workinags fingers coming into contact accidentally with the I, For accomplishing these purposes, a finger grip 20 is fixed securely on the blade. The grip holds a leaf spring 21 on the blade in an operative condition such that, when the blade is in open position, it is yieldably restrained from closure with sufficient resistance to prevent accidental closure of the switch by vibrations. Further, the spring 21 is of electrically insulating material and overlies the rear of the blade and its supportand. thus shields againstaccidental contact with the blade and of the operators fingers. Finally, the blade is provided with a retainer 22 which engages the annular washer portion of the screw 17 so as to hold it captive to the blade while permitting it to be screwed and unscrewed from the stationary contact. y p F The leaf sprin 21 has one portion 23 secured in fixed position with respect to the blade. In the form illustrated, this portion is that adjacent to the grip 20 and is integral with the grip. The leaf spring has another portion '24 which extends from the portion 23, away from the grip to, and engages, the upper ends of the yoke arms 12 under resilient pressure. The pressute is such that when the blade is in an open position of or more, -it is yieldably restrained by the leaf spring 21 from closing. For holding the screw 17 captive a retainer 22 is provided. The retainer 22 has a portion 25, adjacent the grip 20, which is securedin fixed position relativeto the blade. The retainer 22 has aifee end portion 25 is fif= ranged to overhang a part of the screw 17,so as to hold it captive. In the form illustrated, the screw head has a peripheral flange 27 which is engaged'by the outer free end of the retainer 22 to prevent the loss of the screw. The'leaf spring21, the retainer 22, and the grip 20, overlie the rear of the blade ai'idits sup ort, except where the head of the screw 17 .is exposed.

For simplification, the grip 20 is used to hold the leaf spring 21 and retainer 22 firmly in fixed position onthe blade when the grip itself is firmly fixed onto the blade. For holding the grip in firmly fixed position on the blade, the blade is provided with a rearwardly extending integral finger Having teeth 31 thereon. The grip'is provided with a socket 32 arranged to receive the finger 30. The teeth 31 are so arranged that when the grip is installed, they dig into its side walls to prevent its removal. This is desirable because, upon opening the switch blade, the spring tends to urge the grip rearwardly of the blade olfofthefinger30. U 1

It is apparent that with the retainer and leaf spring dis esed between the grip and blade, the grip itself can s erm to hold them firmly in place However, manure a more solid structure and one whieh can be readily as semble'cl and disassembled the grip 20,1af spring 21, and retainer 22, are made integral and composed of elet'rically insulating set, resilient, but surf, synthetic organic plastic. The specific plastic is secondary, though nylon is preferred.

Thus the finger grip 20, leaf spring 21, and retainer 22 can be molded into a single integral unit then, after the switch blade is installed'in the body and the screw 17 installed in the free end of the switch blade, the grip can be placed on the finger and secured firmly thereto, thus holding itself, the leaf spring, and the retainer in operative position. In this position, since theyare of electrically insulating material, they perform not only their primary functions, but also act as ashield to guard against accidental contact of the fingers of the operator with the electrically conducting parts of the switch, except for the exposed for convenience in use. I Having thus described our invention, We claim:

1. A knife switch comprising a body of insulating material, a stationary contact thereon, a switch blade support 'wardly of the blade in shielding relation to the blade sup- ,7

i on the'body, a switch blade pivotally mounted on the blade support for swinging forwardly into, and rearwardly out of, contact with the stationary contact, a finger grip of insulating material connected to the blade, a leaf spring disposed rearwardly of the blade and having a first portion secured in fixed relation to the blade at a location spaced endwise of the blade from the pivotal axis, and having a second resilient portion movable forwardly and rearwardly relative to the blade and extending from the first portion endwise of the blade back to the support, said second portion being in resilientpressure engagement with the support in an open position of the blade and yieldablyresistifig movement of the blade from said open position toward closed position, and said spring being of electrically insulating material and being disposed rearport and blade.

2. A knife switch comprising a body of insulating material, a stationary contact thereon, a switch blade support on the'body, a switch blade'pivotally'mount'ed at one end on the blade support, for swinging forwardly into contact with the stationary contact and rearwardly out of contact therewith, afinger gripof insulating material connected to the blade and disposed rearwardly thereof,

said stationary contact having a threaded aperture, said blade having it free end with an aperture therein, a screw in the-blade aperture and having a threaded shank exposed Y -,at the front ofthe blade and cooperablewith thethreaded aperture of-the contact, when the blade is moved partway tionary contact has a threaded aperture, said blade has a toward closed position, said screw having a head exposed rearwardly of the blade, and a retainer integral with the grip and held thereby on the blade at the rear of the .blade and engaging the screw and holding it captive to the blade in all positions ofthe blade.

3. A structure according to claim 1 wherein the second Q p'ortion of the leaf spring is a strip of set, relatively stiff,

res'ili' 'ltsynthetic organic plastic material which is electrically insu atirig. 1 a a 4. A structure according to clainrl wherein the finger grip and leafspring are integral with each other.

- 5.-A structure according to claim 1 wherein the blade has'a rigid rearwardly, extending finger, the grip is a cap which-is received on the finger and is tightly secured in fixed relation thereto, said first portion of the leaf spring is fixedly connectedtd the cap, and the cap and first portion are of electrically insulating material. 6. A structure according to claim 5 wherein the cap and leaf spring. are integral and are composed of set synthetic organic'plastic insulating material.

7. A structure according to claim 1 wherein said Stafree end with an aperture-therein, a screw is in the blade aperture and has a threaded shank exposed forwardly of the blade and eooperable with the threaded aperture of the contact, when the blade is moved partway toward closed positiom'for drawing the blade firmly into closed position,said screw has a head exposed rearwardly of the blade,'a retainer is carried by the blade and engages the screw and-holds it captive to the blade in all positions of the blade, said retainer being of electrically insulating material, and said spring, retainer, and grip, combined, are in shielding'relation, rearwardly of the blade, to the blade support and to the blade from the blade support to the head of the screw. Y

8. The structure according to claim 7 wherein the leaf I spring, the finger grip, and the retainer are integral.

a head exposed rearwardly of the blade, a rigid finger on the blade and extending rearwardly therefrom, a finger grip in the form of an insulating cap secured on, and covering, the finger, a leaf spring integral with the cap and extending along the rear of the blade away from the free end of the blade to the support and engaging the support in resilient pressure contact, and a retainer integral with the eap and extending therefrom along the rear of the blade toward the free end of the blade and engaging a portion of the screw head and thereby holding the 10 screw captive to the blade.

References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS 3/03 Great Britain; 4/19 Great Britain.

BERNARD A. GILHEANY, Primary Examiner. 

1. A KNIFE SWITCH COMPRISING A BODY OF INSULATING MATERIAL, A STATIONARY CONTACT THEREON, A SWITCH BLADE SUPPORT ON THE BODY, A SWITCH BLADE PIVOTALLY MOUNTED ON THE BLADE SUPPORT FOR SWINGING FORWARDLY INTO, AND REARWARDLY OUT OF, CONTACT WITH THE STATIONARY CONTACT, A FINGER GRIP OF INSULATING MATERIAL CONNECTED TO THE BLADE, A LEAF SPRING DISPOSED REARWARDLY OF THE BLADE AND HAVING A FIRST PORTION SECURED IN FIXED RELATION TO THE BLADE AT A LOCATION SPACED ENDWISE OF THE BLADE FROM THE PIVOTAL AXIS, AND HAVING A SECOND RESILIENT PORTION MOVABLE FORWARDLY AND REARWARDLY RELATIVE TO THE BLADE AND EXTENDING FROM THE 